This invention relates to an anti-knock device for controlling the ignition timing of an internal combustion engine, and more particularly to an improved arrangement for delaying and advancing the ignition timing in response to a knocking signal and at least one sensed running condition of the engine.
As is well known, ignition systems have been proposed that control the timing of the firing of the spark plugs of an engine in response to various engine conditions. Frequently, the spark timing is controlled in response to such factors as engine speed and throttle opening. Both mechanical and electronic systems have been provided for controlling the spark timing of the cylinders of a multi-cylinder engine.
Devices have also been proposed for suppressing engine knocking which can occur, for example, when engine timing is advanced to improve the power output of the engine. Such devices typically operate to retard the ignition timing when knocking occurs. However, in such anti-knock devices the ignition timing is usually advanced to its original timing within a set period of time or soon after the knocking is suppressed by the ignition delay. This can lead to the undesirable phenomenon known as hunting, in which the ignition timing is repeatedly retarded and then advanced. Japanese application 59-213946 proposed an arrangement wherein the time interval between the retarding and advancing of the ignition timing is increased by maintaining the retarded ignition timing for a certain period of time. While this arrangement generally reduces hunting to some extent, it tends to produce an unexpected and sudden change of the ignition timing, causing a sudden fluctuation in engine output. This sudden change in engine operation can, in turn, produce an uncomfortable environment in which to operate the engine.
It is, therefore, a principal object of this invention to provide an improved anti-knock device for an internal combustion engine which suppresses engine knock and reduces hunting, but does not produce an unexpected and sudden change in engine output and speed so as to provide a safer and more comfortable environment in which to operate the engine.